1) Field of the Invention
The present invention relates to a method for forming a metal pattern by using metal nanocrystals, and more particularly to a method for forming a metal pattern by use of a photosensitive compound having a substituent, which is converted into a free carboxyl group by light exposure.
2) Description of the Related Art
With increasing demand for large display area and high resolution of flat panel displays, e.g., liquid crystal displays (LCD), plasma display panels (PDP), and inorganic and organic light-emitting displays (OLED), metal wirings are considerably extended in length and the design rule for the increased aperture ratio is decreased. For these reasons, there arise many problems, such as a significant increase in wiring resistance and capacitance, and signal delay and distortion. Under this circumstance, development of a process for forming a highly conductive metal wiring is recognized to be absolutely essential in developing high resolution and large area flat panel display devices. The use of low resistivity aluminum (Al) as a wiring material has been actively discussed in large-sized LCD. In this case, AlNd, one type of Al-alloy, is used to prevent the problem of wiring non-uniformity, for example, hillocks, due to a substance migration caused when pure Al is used. Meanwhile, because of an increase in resistivity caused by the addition of an alloy and an increase in contact resistance by a high reactivity with α-Si or ITO, a multilayer structure, such as Cr/AlNd/Cr, is required when an Al-alloy is used as a source/drain electrode material.
However, complicated processes are required to form the multilayer structure, and there is thus a limitation in productivity. Metals usable to form metal wirings are presented in the Periodic Table shown in FIG. 2.
Al-alloys are mainly used, but copper (Cu) and silver (Ag) have been the focus of intense interest lately due to their low resistivity and good contact properties on an amorphous silicon layer. However, when copper or silver is used as a gate electrode, it exhibits poor adhesion to an underlying substrate and thus the metal wiring to strip off during subsequent processes. Further, when copper or silver is used as a source or drain electrode, copper atoms are diffused into an amorphous silicon layer at 200° C. or higher or electromigration takes place due to electric drive, causing deterioration in wiring and device properties. Accordingly, in order to use copper or silver as a low-resistivity wiring material, there is a need to form an additional metal layer having good adhesion to a substrate and a low contact resistance in the lower portion and/or the upper portion of the wiring material, leading to a multilayer metal pattern.
In order to satisfy the need to form a large display area at a relatively low cost, it is thus necessary to develop techniques for replacing conventional wiring materials with new materials and forming a multilayer metal wiring in a relatively simple manner.
A method for forming a metal pattern by using a photoresist is currently used. However, since this method involves complex processes, including metal sputtering, photoresist patterning by light exposure and developing, and etching, it is not suitable for use in the formation of a multilayer metal pattern. In addition, technical difficulties and increased manufacturing costs associated with the development of vacuum thin-film deposition equipment according to increasing size of glass substrates for forming large-area patterns, are not trivial.
In this connection, Japanese Patent Laid-open No. Hei 11-119675 discloses a process for producing an electromagnetic wave shielding plate arranged on the front surface of a display wherein a mesh made of a metal thin film is laminated on one side of a transparent substrate. This process is suitable for mass production of an electromagnetic wave shielding plate with superior electromagnetic wave shielding properties and see-through properties. Specifically, the process comprises the steps of (a) forming (masking) a plating resist mask for plating a mesh on a continuous hoop-shaped substrate having plating stripping properties, (b) electrodepositing a metal thin-film layer made of a particular material for mesh formation on portions of the substrate surface exposed from the resist mask, and (c) adhering and transferring the electrodeposited metal thin-film layer to a surface of the transparent substrate for the electromagnetic wave shielding plate using an adhesive. The process is disadvantageous in terms of complicated production steps.
Japanese Patent Laid-open No. Hei 5-16281 discloses a light-transmitting electromagnetic wave shielding material comprising a substrate, a hydrophilic transparent resin layer laminated on the substrate and an electroless plating layer laminated on a pattern of the resin layer wherein a black pattern section is formed between the electroless plating layer and the hydrophilic transparent resin layer. However, the shielding material suffers from the drawback that photoresist and etching processes are accompanied.
Japanese Patent Laid-open No. 2003-109435 discloses a method for producing a transparent conductive film comprising forming a metallic ultrafine particle catalyst layer having a prescribed pattern on a transparent substrate, and forming a metal layer on the catalyst layer wherein the ratio of the average opening diameter to the average line width of the pattern is above 7:1. However, a drawback of this method is the use of the ultrafine catalyst.
There is thus a need in the art for a method that enables the formation of a metal pattern in a cost-effective and simple manner.